The recent research on aldosterone has revealed that said hormone is produced not only by adrenal gland but also by other various organs such as heart, blood vessel or brain, and that its receptor is also widely distributed not only in cardiovascular tissue but also in other tissues. Further, aldosterone has been recognized not only as an exacerbation factor of hypertension, but also as a risk hormone which has various injurious actions on cardiovascular tissue. Under these circumstances, an aldosterone receptor antagonist has been found to have features such as a positive action on serious heart failure or acute myocardial infarction in a recent large clinical trial, and thus is expected to be a potential drug useful for establishing an effective therapy for cardiovascular diseases.
Patent Literature 1 discloses a compound of the following general formula [I]:
useful as an aldosterone antagonist. Among the compound [I] disclosed in said Patent Literature 1, for example, a compound of the following formula [A]:
namely, N-[4-(4-fluorophenyl)-2,2-dimethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-7-yl]methanesulfonamide, is expected to be clinically used as an aldosterone receptor antagonist.
As a method for producing the above compound [A], Patent Literature 1 discloses the following synthetic method.

However, the final intermediate (2) in the above method has been confirmed to have a strong mutagenicity by the AMES test, and thus has a problem of carrying safety and health risks when used as a synthetic intermediate of a medicine. Therefore, as a synthetic method for producing the compound [A], it has been desired to establish an industrially advantageous method without carrying the above safety and health risks.
Also, in general, regarding a compound which is expected to be useful as a medicine, it is known that its physical properties (e.g., the presence or absence of an amorphous state, a crystal and a polymorph thereof, etc.) significantly affect the purity or stability (e.g., photostability and humidity stability, etc.) as an active pharmaceutical ingredient, the stability in a formulation, and the bioavailability when used as a medicine. Therefore, it is an important problem in the development of a medicine to obtain stably and on an industrial scale a single crystal of a medicinal compound having the above excellent physical properties. However, it is difficult to reasonably predict the presence or absence of a crystal and a polymorph thereof of a certain compound. Meanwhile, Patent Literature 1 discloses that the compound [A] was obtained as a powder material.